These studies are aimed at learning more about the mechanisms of DNA transfer and replication of plasmids (or episomes) such as the F factor and the R factors. The questions that we are specifically trying to answer are whether the origins for transfer and normal vegetative replication are the same, and whether these origins occur at the same site as the nicks in the relaxation complexes described by Helinski and his colleagues. We are using methods which will require the development of partial denaturation amps with the electron microscope, and also the digestion of plasmids with restriction endonucleases such as Rl. We are also screening a large number of clinically isolated R factors to determine whether a new class of restriction-modification specificity can be obtained.